As a method for encoding a moving image, moving picture experts group-2 (MPEG-2) which is developed in International Standardization Organization/International Electrotechnical Commission (ISO/IEC) is widely used. Further, H.264/MPEG-4 advanced video coding (H.264/AVC) which is developed in International Telecommunication Union Telecommunication Standardization Sector (ITU-T) which establishes international standards for communication is also widely used.
These encoding methods correspond to progressive video pictures which are obtained by progressive scanning and depicted in FIG. 19 and interlaced video pictures which are obtained by interlaced scanning by every other line and depicted in FIG. 19, as video picture materials. Encoding of a moving image includes frame encoding (progressive encoding) and field encoding depicted in FIG. 20. Encoding is performed by using a video picture which is obtained by taking out all vertical lines of one frame without any gaps in the frame encoding, and encoding is performed by using a video picture which is obtained by taking out every other line of one frame in the field encoding. In the field encoding, there are top field encoding and bottom field encoding depending on a taking position of a video picture.
Here, individual encoding methods support different encoding techniques, so that encoding efficiency differs and calculation amounts of encoding processing and decoding processing differ as well. Accordingly, there is a case where only an encoding method of which a calculation amount is relatively small is supported in a device of which a hardware resource is limited, such as a portable telephone and a portable information terminal. Therefore, a moving image reencoding device (referred to also as a transcoder) which decodes moving image data which has been once encoded by a first encoding method and reencodes the decoded moving image data in accordance with a second encoding method has been developed. For example, in Japanese Laid-open Patent Publication No. 2009-212608, a transcoder that is capable of switching a field encoding mode and a frame encoding mode when reencoding moving image data, which has been encoded in accordance with MPEG-2, in accordance with H.264 MPEG-4 AVC is proposed.